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Old 11-30-2020, 04:22 PM   #1
jhornbr225
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Join Date: Aug 2015
Posts: 18
Default Starting my EZGO Marathon Lithium build.

Finally getting around to posting my build.

I have a 1993 (I believe) Marathon 3 Wheeler. I picked it up about 5 years ago, put a set of 6, 6V Trojans in it, and the wife and I use it around the yard. We have 5 Acres, pretty flat. Mostly I got it for running around the yard, and running to the neighbors the back way. Since it's electric and silent, it's great for going over to the neighbors, and if we leave late at night, there's no gas engine running to wake anybody up. Also, if the wife uses it, and she has an adult beverage, she's not on the road with her car, to go 700 feet.

We dubbed it "Marty" as in, "Marty the Party Cart". Its no looker, but it gets the job done.

As well as new batteries 5 years ago, I installed a 36V-12V power converter, and added some LED headlights.

Over the past year, it's started to need water in the batteries. No big deal, but here late in the fall, the wife left the key on a couple times, which I thought killed the batteries. When it would move, you would push the pedal down, and all the sudden it would JUMP at full speed. A little research led me to believe the batteries were shot. Then it got to the point it wouldn't move at all.

I decided to go Lithium, and upgrade to 48V (ish). I picked a list of parts, and got them ordered. So far:

Alltrax 48500
SW200 Main Contactor
SW202 Reversing Contactors
Precharge Resistor and Diodes
Qty 4 5S BMW 75Ah batteries
Qty 2 4S BMW 75Ah batteries (All of these will parallel together to make a 150Ah 14S Battery.) I got these from BatteryHookup.
14S BMS from BatteryHookup. (It's supposed to have low temp cutoff)
Parts to build the LV and HV monitoring circuit (ala Sergio)
10A 14S Charger
35A DC to DC converter
New Radio
Plum Quick Widowmaker Motor

I had done a little troubleshooting, and found that the reason it wouldn't move on it's own was that I believe the original Curtis controller gave out. I jacked up the rear end, and used 2 of the batteries (12V), through the reversing switch, and the motor turned. I also found out that I have the Blue GE motor, which from my research is 36V only, and not as strong as the AMD motor.

I have pulled all the batteries out, and I see I have some cleanup and painting to do. Yesterday I pulled the motor to confirm it's the 19 Spline. I also played with battery layouts to minimize the fabrication needed. I think by moving the pot box around, and relocating a diagonal brace to give me 1/4" more room, I think they will all fit. Once the diagonal brace in the last pic is moved, that askew battery will sit flat.

I think so far the biggest challenge will be top-balancing the batteries, and hooking good sized wires to actually parallel up the cells. The busbars in these batteries are welded in, so my options for paralleling up cells will require creativity.
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Old 11-30-2020, 04:51 PM   #2
jhornbr225
Not Yet Wild
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Join Date: Aug 2015
Posts: 18
Default Re: Starting my EZGO Marathon Lithium build.

Here's the batteries.

I was originally thinking of cutting a slit in the busbar, and then bending it up to make a tab that I could drill a hole in. That does have the possibility of creating a flimsy, bending tab. I also have to be careful of how close I get to the main terminals for the pack. Battery Hookup sends some very nice cables with plugs on them to tie the batteries in series, or to make connections. Of all these plugs, I have 5 that are 90 plugs. Those will come in handy, especially on the two 4S batteries, where space is a little tight. Now I'm thinking of cutting a 1/2" slit on each side of the "arch", then sliding a plate that has a couple holes in it through the slit. Then I can take an identical plate from the top, and "clamp" down onto the arch. With that method, I am cutting parallel to the cell, and not down into it. Less chance of an error causing a big problem. Attached is a rough sketch of my idea.

These plates wont be the primary current path, they'll be like a busbar extension, so that essentially I'll have a 14S4P battery pack. I'll also attach my balance leads to those tie points as well. Each individual battery is already either a 5S2P or a 4S2P respectively.

When ordering batteries, my original plan was to use two completely parallel strings, with two BMS units. After some more reading, I have decided to go with just one BMS, and parallel up the cells. That avoids some nasty problems. After reading this document, I changed my mind.

https://www.orionbms.com/manuals/pdf...el_strings.pdf

i know this will present unique challenges compared to the Leaf packs, but that's OK.
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Old 12-11-2020, 06:19 PM   #3
jhornbr225
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Join Date: Aug 2015
Posts: 18
Default Re: Starting my EZGO Marathon Lithium build.

My father-in-laws co-worker is a welder, and they stopped by today to look at Marty and see about the welding required to get the batteries to fit. It actually looks like the one bay where I thought the whole diagonal brace needed moved, has already had a repair, which moved the mounting point of the top of the brace closer to the front of the cart. Although it was fine with the FLA batteries, the 4S lithium is just slightly longer. It's the picture of the single battery hole in the first post. We have an appointment next week to load the cart on the trailer, and take it to his shop.

He was thinking of putting some heat on the brace, and trying to bend it. I think the mounting point is just too far forward. I'm thinking we'll just hit it with the angle grinder on that repaired weld to break it loose, move it back a little, and re-weld it.

We hit it with a hammer today and bent it a little. Now the battery fits down in the slot, but with that edge being too far forward, the battery was sitting too high.

Also by going with the battery layout pictured in the first post, and moving the pot box, I'll be able to keep the factory throttle linkage. That's a win.
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Old 12-17-2020, 04:19 PM   #4
jhornbr225
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Default Re: Starting my EZGO Marathon Lithium build.

I loaded up Marty the other day, and took him over to the welder's house. We ground around the brace, and knocked it loose from the frame. He was then able to weld it back a little further and the battery now fits where it is supposed to. There was also a 90 bracket going to the side fender from the battery tray that was broken loose. So we patched that up as well.

I've been doing some thinking on the batteries, and how to parallel them up. I've drawn it up in CAD, and determined the best rotation of the batteries for easier wiring.

I've also been doing some research into capacitive discharge stud welding. The existing busbars inside the batteries are about .050" thick, from what I can measure with my metal calipers, being careful not to short any cells. If I could have someone CD weld some studs onto the busbars, then I would not have to do any dremel work. If I had some 1/4"-20 studs welded to the existing busbars, I could just run the cables in between the cells to parallel them up. That would save a bunch of time and hassle.

I've reached out to a few places and friends locally to see if they have the capability, or know someone who has the equipment to do that. First I contacted a local fabricator house. I've had them do some work for me before. I know they have a laser to cut metal, but I'm not sure they have a CD stud welder. I also reached out to a friend who runs an auto body shop. I'm sure he's got a small one to pull dents, but I'm not sure if his would be large enough to land a 1/4-20 stud. Lastly I contacted my cousin who owns an HVAC repair business. He runs ductwork, but again, I'm not sure if he would have anything big enough.

Another crazy thought I had today was to not parallel them up at all. Basically have two separate sets of batteries, each with their own BMS. The negative of each set could tie together at the Alltrax, but there would only be one positive cable down to the fuse, but it would be long enough to reach the positive side of either string. I did purchase two BMS's to start with. Since the BMW connectors are so easy to plug in and out, I could have one set of batteries be active, and have the other set be idle/able to charge. If you are running the first set of batteries, and they get low, it would be easy to flip the seat up and move the plug over to the other set of batteries. In that case, two voltmeters in the dash would be nice, one for each set. Also some relay logic would be required to make sure the current active set of batteries/BMS combo would be the one that could shut off the keyswitch in the event of an undervoltage. I would also only want the voltmeters to light up if the keyswitch was on. But an undervoltage event shouldn't cut off the voltmeters either, just the Alltrax controller. There are a few negatives to that method though. Having a second set of batteries, I'd have to make it easy enough so that the wife would be able to swap the cable. Even if the idle set needed charged, it's still capable of releasing a ton of energy in the event of a mishap. Also I'd be carrying around 96 extra pounds of dead weight.
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Old 12-19-2020, 08:01 PM   #5
jhornbr225
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Default Re: Starting my EZGO Marathon Lithium build.

I decided to just go ahead and drill holes and mount aluminum plates.

It takes some time, as all the parts are custom. To fit 10-32 nuts under the humps, I have to file them down to be narrow, and then put a 45 on each side. The nice thing is that under each "hump" in the busbar, it is solid plastic, so the nut slides into place easily. I then drill a hole in the hump, being careful not to go too deep. I slide a piece of paper into the hump so catch any debris, and do a lot of vacuuming. I worked on it Friday afternoon, and all day Saturday, and I am pleased to say I'm half done! Yay! I've done one of the 4S batteries and 2 of the 5S. It took longer to do the first battery, as I was refining my method. Today I made all the nuts at one time, then I made all the plates. Then I drilled the humps, and assembled it. Then I cut the cover so that I could snap it back into place.

Tomorrow I'll continue, but I can't be sure I'll finish. And even with the plates in place, I'm still able to use the BMW plugs and get them to plug in and out. I can even use the straight plugs. It's only the 4S batteries that give a problem with space, as the 5S ones dont require a plate so close to where those plug in.
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Old 01-19-2021, 01:05 PM   #6
jhornbr225
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Join Date: Aug 2015
Posts: 18
Default Re: Starting my EZGO Marathon Lithium build.

I did work on the batteries the following day, and got four out of the six done. I ran out of aluminum bar, so I had to get some more. I did finish making all the nuts I needed. That was the time consuming process.

I see that the new motor arrived. Looking forward to getting going on this again.
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Old 04-20-2021, 09:21 PM   #7
jhornbr225
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Join Date: Aug 2015
Posts: 18
Default Re: Starting my EZGO Marathon Lithium build.

Well, some time has passed, and it's starting to get warm, so the motivation to get this project going has returned.

I discovered that trying to make a 14S string with the way the batteries were was going to be too difficult. So I went back into fabrication mode, and added plates and studs to the 2 remaining plates in each battery. That way I will not have to do tie points that are not mounted to a battery. I think that will make things more stable. Even if I don't use any of the plugs that came with the batteries, that's fine.

I went shopping for 2AWG wire and crimp terminals the other day. At my local electrical supply houses, each 2AWG crimp ring terminal is about $4. I need 40 of those just for the batteries themselves, not to mention some other sizes for the motor and the contactors. I did find 2AWG welding cable for $1.59/foot. I ordered the crimp connectors on Amazon, much cheaper that way.

Unfortunately there is a problem with my detached garage workspace. I noticed that the insulation panels on the ceiling were developing gaps between them. I then noticed that the roof in the middle of the building is sagging, and the garage door rollers are almost all the way out of the holders as the door raises. Also the chimney for the wood burner is leaning. I called a contractor to come out and look at it and give me an estimate, and he says the roof trusses have failed. The top of the south wall is leaning out, and the horizontal part of the trusses has separated. I'm now in the process of cleaning the building out so that it can be worked on. Not to mention there are 51 solar panels on the roof that need removed before any work can start.

Never a dull moment.
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